RU2006342C1 - Method for production of bimetallic ribbed cylinders - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: method includes the steps of cast-iron liner aluminizing and aluminium ribbed jacket casting- in, with cast-iron liner external surface aluminizing effected through metallization. The finished ribbed cylinder is thermally treated at 570 ± 10 C for 5 to 10 hours depending on the wall thickness. The method enables the aluminizing time to be substantially reduced (from 15-20 min to 1 min) with high degree of adhesion of cast iron and aluminium layers. EFFECT: reduced time of treatment. 4 dwg

Description

 The invention relates to mechanical engineering, in particular to methods for manufacturing bimetallic ribbed cylinders of internal combustion engines with air cooling.

It is known that the cylinders of internal combustion engines with air cooling on the outer surface have thin and high ribs designed to enhance cooling of the working surface of the cylinder in the area of friction of the piston rings. In most engines, ribbed cylinders are entirely made of cast iron, as the cheapest and most technologically advanced alloy for casting. But iron ribbed sleeves restrict the possibility of increasing the power of the engine forcing due to the fact that in this case the working surface of the cylinder due to insufficient heat conductivity of iron is overheated above the permissible temperatures that are equal to about 240 ^{° C,} max.

 In addition, the manufacture of cast iron ribbed cylinders from cast iron is associated with the difficulty of obtaining free intercostal slots for air flow. When casting in a sand mold, thin ribs of the mold (rods) are sintered. Their surface in the casting turns out to be rough and with a significant burnout, which is removed by a time-consuming and dust-harmful operation - grinding the gaps between the ribs. Casting ribs of cast iron in a metal mold could provide a high frequency of intercostal surfaces, but is not applicable, since such ribs in the chill mold will not fill well, and will also bleach and become brittle.

To enhance heat transfer while maintaining the strength and wear resistance of cast iron, to obtain a clean surface of the ribs, some automotive and tractor companies for engines use bimetallic cylinders in which the working part of the cylinder is a sleeve made of cast iron, and the outer part together with cooling fins are made of aluminum alloy. As a result, by increasing the thermal conductivity of the aluminum layer obtained lower working surface temperature of the cylinder is approximately 25 ^{° C} and is raised by the engine power with afterburner 8-10 horsepower.

 The methods for producing bimetallic cylinders are different; casting is most often used, in which an aluminum alloy is poured onto a solid cast iron sleeve.

In the manufacture of bimetallic cylinders by casting methods, the problems are:
- obtaining reliable adhesion of aluminum surfacing with the surface of a cast-iron sleeve;
- obtaining a continuous, without gaps, connection of cast iron with aluminum along the height of the cast iron sleeve, which is necessary to ensure sufficiently intense heat transfer from cast iron to aluminum;
- technological process.

An analogue of the alleged invention can be adopted a method of manufacturing bimetallic cylinders, according to which, by machining on the outer surface of a cast-iron sleeve, on which a ribbed shirt is cast, teeth are made. Thus prepared cast iron sleeve is installed in the mold and filled with aluminum alloy by known methods. Due to the teeth, tend to get a strong connection of the layers. The advantage of this method is the strong connection of the cast-iron sleeve and aluminum jacket. An aluminum jacket on a cast-iron sleeve will not rotate, which is inevitable when pouring onto a smooth cast-iron sleeve, since the linear expansion coefficients of cast iron and aluminum are significantly different, namely, aluminum has an expansion of twice that of cast iron, therefore, a gap is inevitable when heating and cooling the cylinder . The gap for the diesel cylinder with an internal cylinder diameter of 105 mm will be the threaded diameter:
23.5 ˙10 ^-6 ˙121˙ 170 -
- 11.6 ˙10 ^-6 ˙121˙170 = 0.25 mm, where 121 mm is the outer diameter of the cast-iron cylinder liner of the GAZ diesel engine at the junction of the layers;
170 - temperature at the junction of layers, ^о С (according to the engine laboratory);
23.5˙10 ^-6 1 / deg - coefficient of linear expansion of aluminum;
11.6˙10 ^-6 1 / deg - coefficient of linear expansion of cast iron.

 This gap is shown in the photograph of the microsection of the layer connection, FIG. 1 x 100.

The disadvantage of the analogue is that the formation of a gap in the connection of the layers is also inevitable and therefore the heat transfer will decrease sharply, since the thermal conductivity coefficient λ of the air gap and with a rough surface, as indicated in the source, is significantly lower than the metal layers and is:
- air at ²⁰⁰ ° C and a layer of 0.13 to 5 mm kg˙kal / m˙ch ^o;
- aluminum 175 kg˙cal / m˙h ^about ;
- iron 40-50 kg˙cal / m˙h ^about ;
- boiler scale 1-3 kg˙cal / m˙h ^about .

 The formation of such a gap between the layers and the oxidation of the surfaces sharply affects the heat transfer and the cylinders overheat. Apparently, for this reason, bimetallic cylinders of this type have not received distribution.

The prototype can be adopted by the method of manufacturing a bimetallic cylinder (cast iron-aluminum) by the alpha process. According to this method, a cast-iron sleeve surface-treated by known methods for removing oxidized film and contaminants is washed by dipping an aluminum alloy of the same composition as for a ribbed shirt into a molten liquid for 15-20 minutes until an aluminum intermetallic compound is formed on the surface of the cast iron and iron. Then, the aluminized sleeve is quickly inserted into the mold and the aluminum alloy is filled in by known methods. This gives an intermediate intermetallic layer with a thickness of 0.02-0.03 mm, which provides a dense and cohesive connection of the layers. The intermetallic layer is characterized by high hardness and fragility, its strength is about 8 kgf / mm ² .

 The disadvantages are complexity, low productivity and high complexity of the process, since the alimony takes 15-20 minutes for each sleeve. Due to these shortcomings, the alpha process for bimetal cylinders is not widespread.

 The aim of the invention is to improve the method of manufacturing bimetallic ribbed cylinders.

 The aim of the invention is to provide a simple method of radiation of a dense and cohesive connection of layers of aluminum and cast iron with less time spent on the liner aluminization.

This goal is achieved by the fact that in the method of manufacturing bimetallic ribbed cylinders, including casting and preparing the surface of a cast iron sleeve, aluminizing its outer surface, casting an outer finned shirt of aluminum alloy onto an aluminized layer of a cast iron sleeve installed in a casting mold, aluminizing the outer surface of the liner is carried out by metallization, and the finished ribbed cylinder is subjected to thermal sintering of the layers in the solid state at a temperature close to the melting temperature a luminium 570 ± 10 ^о С, for 5-10 hours

 Metallization is known as the process of coating products from various materials with a thin layer of metal by spraying it in a molten form using compressed air and diffusion metallization as the saturation of the surface layers of metal products (mainly steel) with various metals: aluminum, chromium, zinc, etc. by diffusing them from the environment at high temperature. The main goal is to increase the heat resistance, corrosion resistance, acid resistance, hardness, wear resistance of products.

 In this solution, the intermediate layer of aluminum due to adhesion forms a tight bond of the contacted surfaces of dissimilar metals: cast iron and aluminum. In this case, liquid aluminum particles flying in the plume of the metallizer, striking the solid surface of the cast iron sleeve, destroy or thin the oxide film and during the subsequent operation of thermal sintering, tight contact of aluminum and cast iron of the sleeve is ensured, and therefore, favorable conditions for diffusion and the formation of chemical compounds are created at the point of contact. Aluminum alloy, cast on an intermediate metallized layer, due to cohesion, since there are homogeneous metals, creates a strong and tight connection of layers of sprayed and cast aluminum.

PRI me R. Cast iron sleeves were made by known methods: centrifugal casting, chill casting, sand casting and machining. To obtain a fused and tight connection of the aluminum and cast iron layers, an intermediate layer of aluminum with a thickness of 0.05-0.5 mm was applied to the outer surface of the cast iron sleeve by metallization. A batch of sleeves was installed on the site and metalized using aluminum wire. The temperature of the process is ≈ 800 ^о С. The metallization of one sleeve required 1 min.

 After metallization, the sleeves were installed in the mold and a ribbed aluminum jacket was poured under low pressure (it can also be poured in another known way: in a sand mold, under high pressure).

Constructed thus bimetallic cylinders in the solid state layers was thermally sintered at a temperature close to the melting temperature of aluminum, provided the solid state layers caking iron and aluminum, in this case a temperature of 570 adopted + 10 ° ^C. The holding time at this temperature should be 5-10 hours depending on the wall thickness.

Lowering the temperature <560 ^{° C} did not provide a tight connection layers increase> 580 ^{° C} caused the melting.

 At a shutter speed of <5 h, a dense connection of the layers also did not always turn out, an increase in the shutter speed is technologically impractical. The photomicrostructures of the sintered layers are shown in FIG. 2, in which the cohesion of the compound is visible, in FIG. 3 is a micrograph of the layers prior to sintering, where all 3 layers have interfaces.

 The bimetallic cylinder manufactured by the proposed method for a GAZ diesel engine with air cooling GAZ-542.10 is shown in FIG. 4.

 A batch of bimetallic cylinders was manufactured for laboratory and bench tests. The following results were obtained: all cylinders had a tight connection of layers. The method is simple to implement; time for aluminizing one sleeve ≈ 1 min.

 The mass of the cast-iron cylinder is 7.450 kg, the mass of the bimetallic cylinder is 4.745 kg, i.e. cylinder mass reduced by 36%; the temperature on the mirror of the cylinders (working surface) decreases by 18-31% in comparison with cast-iron cylinders due to increased thermal conductivity of the ribbed part, the temperature regime along the generatrix of the cylinder is stabilized, and temperature stresses in the cylinder are reduced. The payload of the car increases due to lower engine mass, engine power is increased by 8-10 liters. with. due to afterburner. The future of engine building belongs to bimetallic cylinders.

 The analysis and tests showed that the proposed solution meets the criteria of novelty, inventive step and industrial applicability. (56) Japanese Patent N 48-175756, CL 11 B 083, 1973.

Claims (1)

METHOD FOR PRODUCING BIMETALLIC RIBBED CYLINDERS, including casting and preparing the surface of a cast iron sleeve, applying an intermediate layer of aluminum to its outer surface, installing a cast iron sleeve in a casting mold, pouring an aluminum alloy into it to form the outer ribbed shirt, characterized in that the intermediate layer is aluminum applied by metallization, and the finished ribbed cylinder is subjected to heat treatment in the solid state at (570 ± 10) ^o C for 5 to 10 hours

Images